Nuclear reactor comprising a core cover

ABSTRACT

A core cover is carried by an inner rotating shield plug which is mounted in eccentric relation to an outer rotating shield plug and is smaller in diameter than the outer plug and the reactor core. The cover forms above the core a lateral projection with respect to the inner plug. The rotation of the inner plug about its own axis is intended to free part of the reactor core so as to permit handling of fuel assemblies within the core by means of an articulated handling arm which is carried by the outer plug.

[ NOV. 20, 1973 United States Patent 11 1 Aubert [54] NUCLEAR REACTORCOMPRISING A 11/1967 Frame et 176/30 X FOREIGN PATENTS OR APPLICATIONSCORE COVER Inventor: MichelAubert, 6/1959 Fontenay-Aux-Roses, Francel/l967 Netherlands..........................

[73] Assignee: Commissariat A LEnergie Primary Examiner-Carl D.Quarforth Assistant Examiner-E. E. Lehmann Att0rneyWilliam B. Kerkam,Jr.

Atomique, Paris, France Oct. 13, 1971 [22] Filed:

21 Appl. No.: 188,813

[57] ABSTRACT A core cover is carried by an inner rotating shield plugwhich is mounted in eccentric relation to an outer ro- [30] ForeignApplication Priority Data Oct. 15, 1970 France tating shield plug and issmaller in diameter than the outer plug and the reactor core. The coverforms 7 8 l 6 7 I 0 3 6 7 l above the core a lateral projection withrespect to the inner plug. The rotation of the inner plug about its 51Int.

[58] Field of Search own axis is intended to free part of the reactorcore so as to permit handling of fuel assemblies within the core bymeans of an articulated handling arm which is carried by the outer plug.

References Cited UNITED STATES PATENTS 3,044,947 Payne, Jr. 176/30 X3,104,217 9/1963 176/30 5 Claims, 1 Drawing Figure NUCLEAR REACTORCOMPRISING A CORE COVER This invention relates to nuclear reactors,especially of the type comprising a core cover.

In some nuclear reactors and particularly those in the fast-neutronenergy range, provision is usually made above the top portion of thereactor-core fuel assemblies for a structure which is referred-to as a"core cover" and supports instruments such as thermocouples, ebullitiondetectors, burst-can locating devices and the like, these differentinstruments being provided with extensions through a top sealing slab ofthe biological shield of vault which surrounds the reactor and beingconnected to external measuring and monitoring devices. In particular, astructure of this type must extend over the entire top surface of thereactor core since the majority of these instruments such as thethermocouples must correspond in number to the fuel assemblies and mustbe placed in vertically opposite relation to each of these latter. itmust also be possible by means of this structure to gain access to thefuel assemblies which are contained in the reactor core, particularlyfor refuelling purposes. The structure must consequently be movable inorder to free the top portion of the reactor core and thus make itpossible to carry out the corresponding handling operations.

The core cover is therefore usually supported by part of a firstrotating shield plug which is mounted eccentrically with respect to thereactor core in order that it may be located above a free space betweenthe core and a containment vessel. Rotation of said plug permits lateralwithdrawal of the cover into said free space and provides access to thefuel assemblies. A rotating plug of this type is carried by the vaultwithin which the reactor core is placed and is supported either directlyor by means of a second shield plug which also rotates within the wallof the reactor vault and is disposed coaxially with the reactor core.

By reason of the size of the core cover and whatever method may beadopted for supporting the rotating shield plugs, the first shield plugwhich carries the cover must be displaced off-center to a substantialextent with respect to the reactor core and therefore with respect tothe second shield plug. A substantial space must therefore be left freearound said core for the displacement of the cover during refuelling.This makes it necessary to construct a reactor vessel which has verylarge dimensions with respect to the reactor core and in which theunused space during normal reactor operation is considerable.

The aim of this invention is to overcome the abovementioned disadvantageby means of a nuclear reactor design in which the rotating shield plugshave relatively small diameters and only a small free space is providedaround the reactor core whilst the shape and dimensions of the corecover remain normal.

The nuclear reactor in accordance with the invention which comprises acore cover, two rotatable shield plugs including an inner plug whichsupports the cover by means of an axial extension and is mountedeccentrically in the second rotating shield plug or so-called outer plugwhich is larger in diameter and disposed in coaxial relation to thereactor core, and a fuel-assembly handling flask mounted laterally withrespect to said reactor core, is characterized in that the inner plugwhich is carried by said inner plug forms above the reactor core alateral projection with respect to said plug, the rotation of the innerplug about its own axis being intended to expose part of the reactorcore so as to permit handling of fuel assemblies within the core bymeans of an articulated handling arm which is carried by the outer plug.

The combination of the movement of the articulated arm which is carriedby the outer plug and rotational movement of said plug ensure thathandling of fuel assemblies which are placed in a number of differentfuel channels is carried out in one orientation of the shield plugs withrespect to one another thus makes it possible to leave part of the coresurface free and to suspend the cover from the inner plug which issmaller in diameter than the outer plug. Moreover, thetemperaturemeasuring devices and the like can readily be groupedtogether above the cover within the single inner plug despite the smalldiameter of this latter.

The different advantages and properties of the invention will be shownmore clearly in the following description of one embodiment which isgiven by way of non-limitative example, reference being made to thesingle FIGURE of the accompanying drawing which is an axial sectionalview of a nuclear reactor in accordance with the invention.

The nuclear reactor which is illustrated in this F IG- URE is a fastreactor of the upward coolant flow type. In a reactor of this type, thecore 1 is placed within a vessel 2 which is in turn surrounded by aconcrete biological shield structure 4, the vessel 2 andd the concreteshield 4 being closed by a rotatable shield plug or outer plug 6disposed in coaxial relation to the reactor core within which isrotatably mounted a second shield plug or inner plug 8 having a smallerdiametrical dimension. The reactor core 1 proper is surrounded by alateral blanket 14 having an external diameter which is substantiallyequal to that of the outer plug 6. A core cover 10 serves as a collectorfor all the instruments and devices which are intended for measurementsor tests to be carried out on the fuel assemblies of the reactor core las a lateral extension which as a result of rotation of the inner plugexposes part of the reactor core. Said cover 10 is supported on one sideby an extension 9 of the inner plug 8, the diameter of said extensionand of said inner plug being distinctly smaller than that of the coverand therefore of the reactor core. The external surfaces of these twoelements, namely the extension 9 and cover 10, are preferably tangent toeach other internally. Control rod guide tubes 12 and the drivemechanisms for these latter pass through the shield plugs 6 and 8, arespaced at intervals within each plug and are movable downwardly to enterrectilinear passageways 11 in the core cover 10 when in alignmenttherewith as seen for the right guide tube 12 in the drawing without anymechanical connection between said guide tubesand said passageways.

The outer shield plug 6 carries an extensible handling arm 20 in whicharticulated link-rods 21 adjust the position of 'a grappling system 22.The pivotal motion of said link-rods and consequently of the system 22with respect to the arm in conjunction with the rotation of the shieldplug 6 which carries said arm permits displacement of the fuelassemblies contained in the different core channels 18 and transfer ofsaid fuel assemblies to or from a fuel-handling flask 24 which is parallel to said core channels but is placed outside the radial blanket l4.Said handling flask 24 is supported by a device 26 which is capable ofmoving within a discharge duct 28, said duct being secured within thetop wall 4 or biological shield roof in proximity to but outside theouter shield plug 6.

During normal operation of the reactor, the core cover is in theposition shown in chain-dotted lines in the FIGURE, the passageway 11,the guide tubes 12 and the control-rod channels within the reactor beingin aligned relation whilst the measuring instruments are each located inalignment with to a core channel 18 containing a fuel assembly andcarried by the cover 10. When the inner plug 8 is driven in rotationabout its axis 16, said plug causes a displacement of said cover 10 to aposition of withdrawal which is shown in full lines in the FIGURE. Partof the core channels 18 which contain the fuel assemblies is exposed andconsequently made readily accessible. As a result of rotation of theouter plug 6, the handling arm 20 can then be displaced above thereactor core within the space which has thus been freed and thegrappling system 22 can be brought successively above each core channel18 and then above the handling flask 24. Since said rotation of theouter plug 6 is accompanied by the rotation of the inner plug 8, all thecore channels of the reactor can be serviced successively after a singlerotation of the inner plug 8 with respect to the outer plug 6 through anangle of 180.

When the fuel-assembly handling operations are completed, it is onlynecessary to cause a further pivotal movement of the inner plug 8 inorder to replace the cover 10 above the reactor core and to re-positionthe guide tubes 12 opposite to the passageways 11 which form extensionsof said tubes opposite to the corresponding channels within the reactorcore 1. Similarly, the measuring and testing instruments are againlocated opposite to the corresponding fuel assemblies. The control rodscan be lifted and the reactor can be put back into operation.

The reactor core 1 and the radial blanket 14 of this latter aresurrounded within the reactor vessel 2 by a neutron shield whichcomprises a lateral wall 30 having a top shield extension which, in theembodiment shown, is disposed immediately above the core cover 10. Thistop shield is constituted by a plate 32 which is suspended from theouter plug 6 and penetrated by an opening 34 through which the extension9 of the inner plug 8 is intended to pass. In addition, said top shieldcomprises a disc 36 which is contained within said extension 9 androtates with this latter in the same manner as the plate 32 rotates withthe outer plug 6. Finally, the plate 32 is penetrated by a radialpassage 38 for the insertion of the extensible arm 20 which permitslateral movement of the grappling system 22 towards the core channels 18and towards the handling flask 24. Refuelling operations can thus becarried out without either displacing or withdrawing the top shieldelements 32, 36.

In some cases however, the lateral walls 30 of the neutron shield areextended above the handling arm 20 to a level in the vicinity of theconcrete shield roof 4. The top wall of the neutron shield which isplaced immediately beneath said concrete shield roof 4 is alsoconstructed in two sections 32, 36 and each section to one of the shieldplugs 6, 8; however, the radial passage 38 is dispensed with and thehandling arm can be either of the extensible or rotating type. In thiscase the lateral wall 30 is transferred beyond the discharge duct 28 andhandling flask 24 which are thus located within the interior of theshielding and the same applies to the handling arm 20. However, thisshielding only surrounds the space which is strictly necessary for thehandling elements, the lateral blanket and the reactor core.

Moreover, that portion of the core cover which projects on one side ofthe inner shield plug and is placed beneath the outer shield plug playsa part in guiding the control rod mechanisms and in supporting thedifferent measuring instruments even while remaining free with respectto the outer plug. In fact, the measuring devices and the like lyingwithin the reactor enclosure are placed within the core cover 10 inorder to correspond to the positions of the core assemblies but areconnected to the exterior of the reactor containment vault whiletraversing only the inner shield plug. Said devices can therefore bereadily displaced, then moved back in position and centered on the corechannels without entailing any need for disconnection. Similarly, thecontrol rod guide tubes which are carried by the outer plug are cut-offand restored solely as a result of rotation of the inner plug afterlifting of the control rod drive mechanisms. Preliminary disassemblyoperations involved prior to fuel handling as well as the operationsrequired to restore the installation are therefore extremely few innumber. In addition, lost space is reduced to a minimum and this isparticularly important in reactors in which the heat exchangers areintegrated within the reactor vessel and containment vault.

A number of different modifications could clearly be made in theembodiment which has just been described without thereby departing fromthe scope of the invention. By way of example, all the control rod guidetubes and drive mechanisms could be carried directly by the inner plug.

What we claim is l. A nuclear reactor comprising a core cover, tworotatable shield plugs including an inner plug which supports the coverby means of an axial extension and is mounted eccentrically within thesecond rotating shield plug or outer plug which is larger in diameterand disposed in coaxial relation to the reactor core, and a fuelassembly handling flask mounted laterally on said outer plug above thereactor core, the inner plug having a smallerdiameter than the reactorcore and the cover forming above the reactor core a lateral projectionwith respect to said plug, the rotation of the inner plug about its ownaxis exposing part of the reactor core for handling of fuel assemblieswithin the core by means of an articulated handling arm carried by theouter plug, rotation of the cover by the inner plug moving the cover outof the axis of rotation of the outer plug.

2. A reactor according to claim 1, said reactor having around the core aneutron shield comprising a top wall extending above the reactor core,said wall being of two separate sections secured respectively to each ofthe two plugs.

3. A reactor according to claim 2, the neutron shield surroundinglaterally the fuel-handling flask and the articulated handling arm.

4. A reactor according to claim .2, the top wall of the neutron shieldbeing immediately above the core cover and having a radial passage forthe displacement of the articulated handling arm.

5. A reactor according to claim 1, including a radial external surfacefor the axial extension and a radial extemal surface for the core cover,the external surface of the axial extension of the inner plug beinginternally tangent to the external surface of the core cover.,

I. I i 1K

1. A nuclear reactor comprising a core cover, two rotatable shield plugsincluding an inner plug which supports the cover by means of an axialextension and is mounted eccentrically within the second rotating shieldplug or outer plug which is larger in diameter and disposed in coaxialrelation to the reactor core, and a fuel-assembly handling flask mountedlaterally on said outer plug above the reactor core, the inner plughaving a smaller diameter than the reactor core and the cover formingabove the reactor core a lateral projection with respect to said plug,the rotation of the inner plug about its own axis exposing part of thereactor core for handling of fuel assemblies within the core by means ofan articulated handling arm carried by the outer plug, rotation of thecover by the inner plug moving the cover out of the axis of rotation ofthe outer plug.
 2. A reactor according to claim 1, said reactor havingaround the core a neutron shield comprising a top wall extending abovethe reactor core, said wall being of two separate sections securedrespectively to each of the two plugs.
 3. A reactor according to claim2, the neutron shield surrounding laterally the fuel-handling flask andthe articulated handling arm.
 4. A reactor according to claim 2, the topwall of the neutron shield being immediately above the core cover andhaving a radial passage for the displacement of the articulated handlingarm.
 5. A reactor according to claim 1, including a radial externalsurface for the axial extension and a radial external surface for thecore cover, the external surface of the axial extension of the innerplug being internally tangent to the external surface of the core cover.